just do what Milly70 suggests. it works.
furthermore, if you have a time machine backup,
1- on finder, cmd+shift+G, then type exactly /System/Library/Extensions
2- enter time machine, go to a date before you updated your itunes (probably you updated your itunes at the same day with your ios, but otherwise, you have to remember the update date for itunes),
3- find AppleUSBEthernetHost.kext file and restrore it.
4- download Kext Utility from the link Milly70 provides a few posts above.
5- run Kext Utility.
6- drag the AppleUSBEthernetHost.kext file into the Kext Utility. It will do the rest of the job.
when Kext Utility finishes, you should be ready to use USB tethering. not sure if you need to restart, but it is not a big deal to do if so.
note: i am using lion. haven't tried it on mountain lion or mavericks. but the key is to use Kext Utility since it arranges some of the settings for the file for the system to identify and use it. otherwise, system alerts an error, sayin, AppleUSBEthernetHost.kext file was not installed properly.